The invention concerns an electric motor and in particular an electric motor having a characteristic function.
Examples of electronically commutated motors are described, for example, in the following documents of the Applicant:
DE 44 41 372 A1 [(internal: D183)]=U.S. Pat. No. 5,845,045 JESKE
EP 0 658 973 B1 [(internal: EP184)]=U.S. Pat. No. 5,590,235 JESKE
DE 296 06 939.6-U [(internal: D190i)]=EP 0 739 084 A2
DE 195 15 944 A1 [(internal: D192)]
EP 0 741 449 A1 [(internal: EP193)]=U.S. Pat. No. 6,163,117
EP 0 744 807 B1 [(internal: EP194)]=U.S. Pat. No. 5,847,523
DE 195 18 991 A1 [(internal: D195)] DIETERLE et al. (publ. Jan. 23, 1997)
DE 196 47 983 A1 [(internal: D199i)]=U.S. Pat. No. 6,091,887
EP 0 780 962 A2 [(internal: EP200)]
It would not be possible to reproduce the extensive content of these documents in the present application even in summarized form, and reference is therefore made to their complete contents.
In DE 44 41 372 A1 and corresponding U.S. Pat. No. 5,845,045, the rotation speed behavior of an electric motor is represented by a characteristic n=f(T), a setpoint speed n being associated with each temperature T. In the case of a fan, for example, the rotation speed can thus be increased as the temperature rises. The rotation speed/temperature behavior is determined, in this context, by analog components. The accuracy achievable here is not great, however, due to manufacturing tolerances in the components, and it is possible only with great effort to switch over to a different behavior.
It is therefore an object of the invention to make available a new electric motor and a method for operating such an electric motor.
According to a first aspect of the invention, this object is achieved by an electric motor having a rotation speed controlled by a changeable physical variable, in particular a temperature; having a characteristic field, stored in the form of individual digital values, for the allocation of values of said physical variable to corresponding rotation speed values of the electric motor; and having a microcontroller or microprocessor which has access to the stored individual digital values. An electric motor of this kind is very versatile, since because of the stored characteristic field its rotation speed behavior as a function of the changeable physical variable can easily be modified. It has proven particularly advantageous in this context to store the individual digital values at least partially in vector form, since this makes them substantially easier to process.
The invention additionally concerns a method for controlling a physical variable, in particular a rotation speed, having the following steps:
a) in order to ascertain the system deviation, a difference is determined between a desired value for the physical variable (in digital form), and an actual value for the physical variable (also in digital form);
b) the sign and absolute value of that difference are ascertained;
c) an analog memory element is charged or discharged, depending on the sign;
d) the duration of the charging or discharging operation is in each case substantially proportional to the magnitude of the ascertained absolute value of the difference;
e) a value dependent on the charge of the analog memory element is used to influence the pulse duty factor of an actuating member that in turn influences, with its output signal, the physical variable that is to be controlled.
The result is to create a highly advantageous combination of digital accuracy in ascertaining the system deviation, and subsequent processing of that system deviation in order to influence the physical variable.
A further way of achieving the stated object is provided by a method for temperature-dependent control of the rotation speed of an electric motor having the following steps:
a) value clusters of characteristic definition points are stored in a memory, said value clusters containing at least one value characterizing a specific temperature, and one rotation speed datum associated with that temperature;
b) a present value characterizing the temperature that controls the motor rotation speed is sensed at time intervals;
c) that sensed value is compared to the stored values that characterize the temperature and are contained in the stored value clusters;
d) a stored value adjacent to the present value is ascertained;
e) by way of an interpolation proceeding from that adjacent value, a rotation speed datum for the sensed present value is ascertained;
f) a value derived from that interpolated rotation speed datum is conveyed to the electric motor.
It is thereby possible, by storing a small number of value clusters, to define the rotation speed behavior of a motor as a function of temperature.
The invention furthermore concerns a method for A/D conversion in an arrangement having a voltage divider containing a temperature-dependent resistor, one tapping point of that voltage divider defining the potential at the one input of a comparator, and the potential at the other input of the comparator being determined by a capacitor that can be charged via a constantcurrent source, having the following steps:
a) first the capacitor is discharged;
b) then a measurement is made of the time required for the capacitor, as it is charged by the constant-current source, to reach the potential of the other input;
c) that time is used as an indication of the temperature of the temperature-dependent resistor.
A method of this kind can easily be implemented using a microcontroller which controls or regulates functions of an electric motor. That microcontroller can effect discharge of the capacitor in step a), and can provide time measurement as defined in step c), the overall result being a very simple method.
Another way of achieving the stated object is provided by an electric motor having discrete values, stored in a memory, which (in the form of support values) define a temperature/rotation speed characteristic, the discrete values being modifiable via a data connection to an input device arranged outside the electric motor. This makes possible simple adaptation of such a motor to different customer requirements.
A further way of achieving the stated object concerns a method for operating an electronically commutated motor having associated with it a microprocessor or microcontroller and a program associated therewith, that program serving to control a plurality of motor functions of different priorities, having the following steps:
a) a plurality of requestable routines necessary for operation of the motor are provided;
b) when a requestable routine is needed, a corresponding request signal for it is set;
c) a higher-level program function is used to check which requested routine has the highest priority, and that highest-priority routine is executed first;
d) following execution of that highest-priority routine, the request signal associated with that routine is reset.
A method of this kind makes very good use of the available computing capacity of a microprocessor or microcontroller, and makes it possible to repeat specific time-critical interrogations or the like at intervals which do not exceed a predefined duration. These can be, for example, interrogations of a data bus by means of which data or instructions can be conveyed to the motor. This method is preferably continuously repeated, in the manner of a loop, while the motor is operating, the loop sequences being different depending on the type of routine requested. It is particularly advantageous in this context if a requestable routine to be executed in the program can in turn generate, during its execution, a request signal for another requestable routine to be executed. This allows close concatenation of routines, between each of which time-critical program steps can be executed.
A further way of achieving the stated object concerns a motor having a microprocessor or microcontroller and a bus, in which the microprocessor or microcontroller controls both the bus and the motor. A motor of this kind is very inexpensive due to the reduction in electronic components, and the elimination of further electronic components moreover makes possible a compact design for the motor. Because the entire control system of the motor is displaced into the microprocessor or microcontroller, it is possible to make changes to the motor merely by changing the software.
Further details and advantageous developments of the invention are evident from the exemplary embodiments which are described below and depicted in the drawingsxe2x80x94and which are to be understood in no way as a limitation of the invention.